Sputtering of a LiF(100) surface by singly and doubly charged Ne ions with impact energies between 10 and 500 eV has been performed. The emission of Li+, Li0, F+, F0 and LiF+ was measured by means of a quadrupole mass spectrometer. The yield of sputtered Li+ ions and Li0 atoms decreases with decreasing impact energy and is slightly higher for Ne2+ compared to Ne+ at impact energies below 100 eV. The situation changes very drastically regarding the emitted F particles. In the whole energy range investigated, the F+ and F0 yield was about one order of magnitude larger if Ne2+ projectiles were used instead of Ne+. According the experimental data we propose following model for the emission of F+: (1) The F- ion of the solid surface is changed to F+ by Auger neutralization of the Ne2+ into Ne+ or by double resonance transition into doubly excited states of Ne0 with subsequent autoionization into Ne+. These processes takes place several Ångström in front of the surface. (2) The initial repulsive forces between the F+ ion and the surface are changed into attractive ones within a very short time by rearrangement of the alkali halide lattice. (3) The neutralized projectile sputters the F+ as in a normal sputtering event on a surface with low surface binding energy, and F+ can be emitted as long as the kinetic energy of the projectile is sufficiently high.
Corresponding author: P. Varga (varga).